1. Field of the Invention.
The present invention relates to a solar cell module and a method of producing it. More specifically, the invention relates to a solar cell module which can be produced at a low cost, which shows a smaller energy conversion efficiency degradation even when the module is partly shaded solar cell module and which is not damaged even when maintained in such state for a long time, and a method of producing such solar cell module. The present invention also relates to a solar cell module that can effectively exhibit a high energy conversion efficiency when installed on a curved surface, and a method of producing such solar cell module.
2. Related Background Art
Solar cells have been widely developed and are starting to be introduced for use in the home, as the environmentally acceptable clean power source. Ordinary electric appliances are usually driven with an alternating current of 100 V. On the other hand, the output of a solar cell is a direct current and an inverter has to be used in order to obtain an alternating current. In such a case the inverter cannot operate efficiently unless the output of the solar cell is at least 100 V. Also when the electric power is stored in a secondary battery, the DC output can be directly used, but the secondary battery is usually used at 12 V to 24 V.
However, a unit cell of a solar cell can only provide an output voltage of 0.5 to 0.6 V, also a unit cell of an amorphous silicon solar cell of a relatively high output voltage can only provide an output voltage of 0.7 to 0.9 V alone, and the tandem cell of plural junctions stacked can only provide an output voltage of about 2 V at maximum. For this reason, the solar cell is usually used as a module in which plural unit cells are connected in series. Such formation of the module by series connection of the unit cells of the solar cell also provides an advantage of reducing the current in the module, thereby remarkably lowering the power loss resulting from electric resistance in the wiring part.
However, during the use of the module with the unit cells connected in series, there may generate a situation where the shade of a wood or a building falls on a certain unit cell of the unit cells constituting the module, whereby only the output of the certain unit cell extremely drops. Such a situation is called a xe2x80x9cpartial shade statexe2x80x9d. In such a partial shade state, the output voltage of the entire module dramatically drops, and in some cases the shaded unit cell merely functions as a load to cause heat generation or is damaged by a strong reverse bias voltage. In this regard, it is known to connect a small diode which is called a bypass diode to a solar cell element (unit cell) in parallel and in an opposite direction thereto, thereby reducing the influence of such a partially shaded state.
FIG. 4 shows the working principle of such a bypass diode, wherein unit solar cells 301 to 304 of the solar cell are connected in series and further connected to an external load 305. In a normal state under irradiation with sunlight 306, there is generated an output voltage equal to the sum of the output voltages of the unit cells 301 to 304 (in FIG. 4, reference character A indicates a terminal at a negative side and B indicates, a terminal at a positive side). However, when the shade of an object 307 falls, for example, on the unit cell 303, the unit cell 303 substantially functions as a load of an extremely high resistance, whereby the output current of the module is reduced and the output voltage is extremely lowered. In addition the unit cell 303 receives, in the opposite direction, the sum of the output voltages of the unit cells 301, 302 and 304, whereby such reverse bias voltage causes abnormal heat generation in the unit cell 303 or damages the unit cell 303 by the reverse electric field.
On the other hand, in the case of providing a bypass diode 303xe2x80x2 with the unit cell 303, the unit cell 303 is short circuited, whereby an originally intended current substantially flows in the entire circuit and the unit cell 303 can be protected from the reverse electric field. When the unit cell 303 functions in the normal state, the bypass diode 303xe2x80x2 is reversely biased, whereby little leak current flows and the function of the module is not affected. The bypass diodes 301xe2x80x2 to 304xe2x80x2 are provided for the unit cells 301 to 304 of the solar cell, respectively, thereby causing damage by the reverse electric field is in a unit cells unit.
However, such bypass diodes are required in the same number as that of the unit cells and therefore the cost and complexity the wiring step for this purpose is appreciable. For example, the Japanese Patent Application Laid-Open No. 3-24768 proposes that the bypass diode is integrally formed with the unit cell. In the prior art, as shown in FIGS. 9, 10, 11A and 11B, n-type diffusion regions are formed on both sides of a p-type with substrate and one of such diffusion regions is utilized as the bypass diode. In these drawings, reference character 20 indicates a p-type silicon substrate; 21 and 22, n-type diffusion layers; 23 and 24, electrodes; SC, a unit cell; BD, a bypass diode; 1, 2 and 3, unit cells; A and B, bypass diodes; C, a bypass diode; and 25, 26, 27 and 28, lead wires. Such a configuration, however, has drawbacks such as requiring a complex series connection step and also requiring one external diode per module. For this reason, the above-mentioned patent application also proposes a method of integrally forming an independent bypass diode in the substrate, as shown in FIGS. 12A, 12B, 13A and 13B. In these drawings, reference characters 61 and 101 indicate p-type silicon substrates; 62 and 102, n+-type diffusion layers; 63 and 103, n-type diffusion regions; 64 and 104, p-type diffusion layers; 65 and 105, oxide films; 66 and 106, oxidation preventing films; 67 and 107, surface electrodes; 68 and 108, back surface electrodes; and 109, a junction short circuit portion. This configuration certainly simplifies the series connection step, but requires an additional semiconductor step for incorporating the diode into the substrate, so that this configuration cannot reduce the total manufacturing cost of the solar cell module.
In consideration of the foregoing, the object of the present invention is to provide a solar cell module of a novel configuration which is capable of minimizing the reduction of the module output without damage in the unit cells even in the partial shade state and which is not complex in the semiconductor step or in the series step, as compared to solar cell module. The case without such countermeasure, and a method of producing such a solar cell module.
According to the view of the present inventors, the structure shown in FIG. 9 is rather advantageous in the prior art term of simplifying the semiconductor step. Namely, the n-type diffusion layers (one being used for the light-receiving region, the other being used for the bypass diode) on both sides of the p-type substrate can be prepared in one step. However, the n-type diffusion layer for the bypass diode has to be thereafter removed except for a necessary area. Also as pointed out in the above-mentioned patent application, it is not easy to form the series connection bridging the top side and the bottom side of the substrates as shown in FIGS. 11A and 11B.
The present inventors have conceived to form the light-receiving portion of the solar cell element and the bypass diode on the same side of the substrate. Such a configuration allows for series connection from only one side of the substrate. The unit cell of such structure, if prepared by a simple method, will provide a countermeasure against the partial shade state at the lowest cost in total.
The present invention provides a solar cell module comprising a plurality of unit cells connected in series, each of the unit cells comprising in this order an electrode, a first semiconductor layer having a first conductivity type and a second semiconductor layer having a second conductivity type, wherein the electrode has a region not covered with the first semiconductor layer, wherein the second semiconductor layer has a main region and a subregion which are separated by a groove, wherein the main region of the second semiconductor layer in one unit cell of the unit cells is electrically connected to the region of the electrode not covered with the first semiconductor layer in another unit cell adjacent to the one unit cell, and wherein the region of the electrode not covered with the first semiconductor layer in the one unit cell is electrically connected to the subregion of the second semiconductor layer in the another unit cell.
In the present invention, the second semiconductor layer is preferably a layer having a low resistance.
Also, the second semiconductor layer is preferably a doped layer having a high dopant density.
Further, it is preferable that the first semiconductor layer is a p-type semiconductor layer and the second semiconductor layer is an n+-type semiconductor layer, or that the first semiconductor layer is an n-type semiconductor layer and the second semiconductor layer is a p+-type semiconductor layer.
Still further, it is preferable that each of the unit cells has a rectangular shape, a long side direction of the rectangular shape is arranged so as to be perpendicular to a generating line of a curved surface represented by a cylindrical surface or a conical surface, and each of the unit cells is connected in series in a direction of the generating line.
Still further, it is preferable that at least one of the first semiconductor layer and the second semiconductor layer is a single-crystalline silicon layer.
The first semiconductor layer is preferably a semiconductor sheet. An electrode plate, a conductive sheet or the like is preferably used as the electrode.
The present invention also provides a solar cell module comprising a plurality of unit cells connected in series, each of the unit cells comprising in this order an electrode, a semiconductor layer and a transparent electrode layer, wherein the electrode has a region not covered with the semiconductor layer, wherein the transparent electrode layer has a main region and a subregion which are separated by a groove, wherein the main region of the transparent electrode layer in one unit cell of the unit cells is electrically connected to the region of the electrode not covered with the semiconductor layer in another unit cell adjacent to the one unit cell, and wherein the region of the electrode not covered with the semiconductor layer in the one unit cell is electrically connected to the subregion of the transparent electrode layer in the another unit cell.
Hereinafter, the region of the electrode not covered with the (first) semiconductor layer is referred to as the xe2x80x9ctabxe2x80x9d in some cases.
The present invention also provides a method of producing a solar cell module, which comprises the steps of:
providing a plurality of unit cells, each of the unit cells being produced by forming a second semiconductor layer having a second conductivity type on one surface of a first semiconductor layer having a first conductivity type, forming a groove in the second semiconductor layer to separate the second semiconductor layer into a main region and a subregion, and forming an electrode having a region not covered with the first semiconductor layer on the other surface of the first semiconductor layer;
adjacently arranging the plurality of unit cells;
electrically connecting the main region of the second semiconductor layer in one unit cell of the unit cells to the region of the electrode not covered with the first semiconductor layer in another unit cell adjacent to the one unit cell;
electrically connecting the region of the electrode not covered with the first semiconductor layer in the one unit cell to the subregion of the second semiconductor layer in the another unit cell.
The present invention also provides a method of producing a solar cell module, which comprises the steps of:
providing a plurality of unit cells, each of the unit cells being produced by forming a transparent electrode layer on one surface of a semiconductor layer, forming a groove in the transparent electrode layer to separate the transparent electrode layer into a main region and a subregion, and forming an electrode having a region not covered with the semiconductor layer on the other surface of the semiconductor layer;
adjacently arranging the plurality of unit cells;
electrically connecting the main region of the transparent electrode layer in one unit cell of the unit cells to the region of the electrode not covered with the semiconductor layer in another unit cell adjacent to the one unit cell;
electrically connecting the region of the electrode not covered with the semiconductor layer in the one unit cell to the subregion of the transparent electrode layer in the another unit cell.
The present invention also provides a method of producing a solar cell module, which comprises the steps of:
providing a plurality of unit cells, each of the unit cells being produced by forming a dopant supplying layer on one surface of a first semiconductor layer having a first conductivity type, forming a groove in the dopant supplying layer to separate the dopant supplying layer into a main region and a subregion, forming a second semiconductor layer having a second conductivity type in the one surface of the first semiconductor layer by diffusing a dopant from the dopant supplying layer, and forming an electrode having a region not covered with the first semiconductor layer on the other surface of the first semiconductor layer;
adjacently arranging the plurality of unit cells;
electrically connecting the main region of the second semiconductor layer in one unit cell of the unit cells to the region of the electrode not covered with the first semiconductor layer in another unit cell adjacent to the one unit cell;
electrically connecting the region of the electrode not covered with the first semiconductor layer in the one unit cell to the subregion of the second semiconductor layer in the another unit cell.
The present invention also provides a method of producing a solar cell module, which comprises the steps of: providing a plurality of unit cells, each of the unit cells being produced by forming a first semiconductor layer having a first conductivity type on an electrode, forming a second semiconductor layer having a second conductivity type on the first semiconductor layer, and forming a groove in the second semiconductor layer to separate the second semiconductor layer into a main region and a subregion, a portion of a surface of the electrode being exposed;
adjacently arranging the plurality of unit cells;
electrically connecting the main region of the second semiconductor layer in one unit cell of the unit cells to the region of the electrode not covered with the first semiconductor layer in another unit cell adjacent to the one unit cell;
electrically connecting the region of the electrode not covered with the first semiconductor layer in the one unit cell to the subregion of the second semiconductor layer in the another unit cell.
In the above method, it is preferable that the first semiconductor layer is formed so that the portion of the surface of the electrode is exposed, or that after the first semiconductor layer is formed, the portion of the surface of the electrode is exposed.
Further, the present invention provides a method of producing a solar cell module, which comprises the steps of:
providing a plurality of unit cells, each of the unit cells being produced by forming a semiconductor layer on an electrode, forming a transparent electrode layer on the semiconductor layer, and forming a groove in the transparent electrode layer to separate the transparent electrode layer into a main region and a subregion, a portion of a surface of the electrode being exposed;
adjacently arranging the plurality of unit cells;
electrically connecting the main region of the transparent electrode layer in one unit cell of the unit cells to the region of the electrode not covered with the semiconductor layer in another unit cell adjacent to the one unit cell;
electrically connecting the region of the electrode not covered with the semiconductor layer in the one unit cell to the subregion of the transparent electrode layer in the another unit cell.
In the above method, it is preferable that the first semiconductor layer is formed so that the portion of the surface of the electrode is exposed, or that after the first semiconductor layer is formed, the portion of the surface of the electrode is exposed.
Additionally, in the above methods of producing a solar cell module, the formation of the groove is preferably conducted by laser scribing.